The present invention pertains to sprinkler systems which are installed in structures for protection against fire, and more particularly pertains to adjustable drop nipples which can be employed during the installation of sprinkler systems wherein the sprinkler heads hang below a ceiling. The present drop nipple can be used to particular advantage with "wet" sprinkler systems, but can also be employed, if preferred, with "dry" sprinkler systems.
When a number of ceiling sprinklers are installed above a room, the water distribution piping is mounted in the space between the ceiling and the next higher floor or roof, and it is extremely difficult, if not impossible, to install both the ceiling of the room and a non-adjustable piping arrangement to precise elevations which, without adjustment, will result in flush alignment of the sprinkler heads with the ceiling panels, since neither can be made perfectly level. More specifically, if all the drop nipples are made up to the same length, some will provide the effect of being too short, and others too long, so that alignment of the sprinkler heads with the ceiling can only be accomplished by customizing the length of the drop nipple at each location, or by use of a drop nipple having an adjustable length.
The making up of each drop nipple to a different length requires considerable time and is, therefore, relatively expensive. This problem has been previously recognized and has been approached by design and use of drop nipples which can be adjusted in length, examples being the adjustable drop nipples disclosed in U.S. Pat. Nos. 3,529,671 and 3,807,503. Each of the drop nipples disclosed therein comprises a first conduit which is inserted in a second conduit, the first conduit being movable axially back and forth in the second for adjusting the length of the assembly. In addition, the prior drop nipples make use of O-ring selas to protect against leakage of water when the sprinkler system is idle. It is nonetheless felt, however, that these prior adjustable drop nipples have certain drawbacks associated with their O-ring seal system and/or the complexity and cost of their manufacture.